Natural and synthetic metal oxide compositions, such as iron oxide, have been used for a variety of applications. For example, it is well known to use of metal oxides, particularly iron oxide (FexOy) and ZnO, in a reactor bed to remove contaminants, typically sulfur compounds, such as hydrogen sulfide (H2S), from fluids, typically gas streams. Sulfur compounds are removed from fluids because they are known contaminants, which potentially make gas streams or other fluids unsalable. Other uses of metal oxides and basic metals includes the removal of arsenic, radioactive isotopes, and halogenated hydrocarbons from water. Metal oxides are also used in a wide range of catalytic processes for chemical production and contaminant removal from various fluids, such as, but not limited to, sulfur compounds, NOx and SOx, CO2.
There are a several processes used for making metal oxides from water-soluble metal salts including hydrothermal synthesis, hydrothermal precipitation, flame hydrolysis, or thermal decomposition. All of these processes, however, include multiple manufacturing steps that can be both costly and time intensive. For example, hydrothermal synthesis includes mixing an iron salt with a base solution, heating the solution with hot water, feeding the solution into a reactor for a sufficient amount of time to produce metal oxide particles, cooling the mixture, separating the metal oxide from the remaining solution, and drying the metal oxide particles. Flame hydrolysis includes vaporizing a metal halide and transporting it in an inert gas into an oxy-hydrogen flame. The metal halide salt decomposes in the water producing flame to produce a metal oxide.
Currently, powder coated metal oxide on substrates are used in flow-through packed-bed processes to react with and scavenge hydrogen sulfide and thiols (mercaptans) present in natural gases and liquid hydrocarbons. There are several processes used to make loosely-adhered powdered metal oxide moistened on substrates. Other processes require binding the metal oxide to a substrate with an adhesive or, calcining or drying a metal oxide mixture onto a substrate. These processes include various manufacturing steps that can be both costly and time intensive. The process of binding the metal oxide to a substrate with an adhesive or binding agents includes, for example, admixing zinc oxide with adhesives and processing the mixture into pellets, spheres, or flakes by extrusion. The calcining process includes soaking a substrate multiple times in soluble metal oxide solutions and calcining or drying to create a specific metal oxide content on the substrate. As such, processes for making a metal oxide composition that is a tightly-adhered coated metal oxide composition substrate and includes fewer manufacturing steps is desired.
The resultant loosely-adhered powdered metal oxide coated substrates currently being produced by simple moistening of the powdered metal oxide on a substrate described in the above processes also have several problems. For example, depending on the adhesive used, if any, to bind the coated metal oxide to the substrate, the coating may degrade or separate from the substrate thereby becoming less effective in the removal of contaminants from fluids. In addition, the moistened powdered metal oxides on substrates produced by current processes have limitations as to the amount of metal oxide that can be coated onto the substrate. Typically, the processes are limited to less than 20% by weight metal oxide content on each substrate. The substrate must be carefully selected as the substrate can be important in maintaining the moistened powder metal oxide on the substrate. Many granular substrates are not suitable as they release the powdered metal oxide from the substrate during storage, drying, or when exposed to excessive moisture. Finally, it is believed that the hardness of the powdered metal oxides wetted on substrates currently is limited to substrates that are already hard and are not further softened by moisture. The substrate hardness is necessary to ensure the final product has sufficient crush strength to be used in a packed bed. This means it is difficult to make a coated product from a lightweight substrate, such as vermiculite and perlite. Additionally, non-porous substrates cannot be used as they resist moistening that allows the metal oxide powder to attach and stick on the substrate. Also, most moisture sensitive substrates like calcium chloride are unavailable. Typically, use of such substrates results in a product that does not maintain its stability in packed-bed reaction vessels. As such, a process for coating a wide variety of substrates that can achieve a high metal oxide content is desired. It is also desired to have a metal mixture on a substrate that is not easily removed.